The case, Arizona v. United States, will not only be the Court’s second politically-charged blockbuster in as many months, but also a rematch between the Solicitor General Donald Verrilli and D.C. superlawyer Paul Clement. Over three days in late March, they faced off over the limits of federal power in the health care cases. This time, they will have a single hour debate over whether states may invade fields of immigration policy the federal government claims to occupy. It will be the justices’ final oral argument of the term.

Specifically at issue are four provisions of the law that the lower courts blocked, finding them likely to conflict with federal immigration laws. Two of the blocked sections make it a crime under state law for an undocumented immigrant to be present in the state, fail to register with the federal government and attempt to obtain work or hold a job without governmental authorization. Another section requires state and local police officers to check the immigration status of anyone who has been arrested, stopped or detained and who the police reasonably suspect to be in the country undocumented. The fourth provision at issue allows police to arrest individuals without a warrant if they have probable cause those individuals have committed deportable offenses.

Clement, who represents Arizona and its governor, Jan Brewer, is trying to unblock these provisions by framing them as “Arizona’s efforts at cooperative law enforcement” with the United States. “President [Barack Obama] fairly describes our Nation’s system of immigration regulation and enforcement as ‘broken,'” Clement wrote in Arizona’s brief. He spends several pages describing the health, safety and economic difficulties Arizona has faced as a result of that “broken” system, citing the state of emergency declared in 2005 by then-Gov. Janet Napolitano, who currently serves as President Barack Obama’s secretary of homeland security.

The United States, however, sees Arizona’s efforts in a less complimentary — and complementary — light. “The framework that the Constitution and Congress have created does not permit the States to adopt their own immigration programs and policies or to set themselves up as rival decisionmakers based on disagreement with the focus and scope of federal enforcement,” Verrilli told the justices in the federal government’s brief.

“[B]y refusing to respect Congress’s designation of the Executive Branch to take the lead in the enforcement of the federal immigration laws, and by requiring all Arizona officers to adhere instead to the State’s own policy of ‘attrition through enforcement,’ Arizona has exceeded the permissible bounds of cooperation,” Verrilli wrote.

Lucas Guttentag, a lecturer in law at Yale and Stanford as well as founding director of the ACLU’s Immigration Rights Project, calls the case a “defining moment for the Court.”

“The arguments and the legal claims are technical, but the implications are sweeping,” Guttentag said. “Core concerns about discrimination and profiling” — in Arizona’s case, against the state’s Hispanic residents, documented or not — “are the reason why the Supreme Court has historically held that states may not intrude into the field of immigration regulation. It leads to discrimination, harassment, interference with foreign relations and an undermining of the national interest in national uniformity.”

The federal government’s brief emphasizes that last consideration. “A scheme that depends on national uniformity cannot coexist with a patchwork of different state regimes, whether that patchwork involves 50 different decisionmakers, 50 different remedies, or 50 different substantive rules,” Verrilli wrote.

Utah, Indiana, Alabama, Georgia and South Carolina have already passed Arizona-style legislation. Eight other state legislatures pose a “serious threat” to do the same and sixteen more have “flirted” with such laws, according to a report by the Center for American Progress, a liberal-leaning think tank.